This invention is related to apparatus for examining an object by means of radiation such as x- or gamma-radiation. More particularly, the invention is concerned with computed tomographic apparatus which provides a complete image corresponding to a cross-section of the beating heart produced on a cathode-ray tube display during a time interval which is a small fraction of the duration of the heart cycle and which corresponds to a specific portion of the heart cycle.
Computerized tomography permits the production of a representation of the variation, over a cross-sectional slice of a body under examination, of the absorption or transmission coefficient with respect to the penetrating radiation, such as X-radiation. Such representations provide a considerable amount of clinically useful information and, in particular, enable tumors or tissue damage to be identified and accurately located without the need for surgery or invasive diagnostic procedures.
Various techniques for performing computerized tomography are described in U.S. Pat. No. 4,035,647 and in U.S. Pat. No. 4,075,492 and other techniques are disclosed in U.S. Pat. No. 4,149,247. The former techniques offer potentially rapid data acquisition employing a fan-shaped beam, and the latter techniques are concerned primarily with the reconstruction method for a fan beam source which employs a convolution method of data reconstruction, without the prior reordering of fan rays, to eliminate errors in the measurements and delay in computation time which would otherwise be involved in such reordering. Rapid data acquisition and fast reconstruction are important because if the data is acquired rapidly, and the tomograph is reconstructed quickly based upon the data acquired, there is less chance of the representation being marred by artifacts due to movement of the body under examination, or of organs or fluids therein, during the acquisition time.
In principle, with the technique described in U.S. Pat. No. 4,035,647 the radiation is constrained to conform to a fan-shaped spread, emanating from a small source area, and the radiation is projected through the body. The fan angle of the spread of radiation is sufficient to embrace at least a substantial part of the slice of the body and the source is rotated around the body about an axis intersecting the slice. The array of detector devices is provided to receive radiation projected through the body and to provide output signals which are sampled at a rapid rate. The individual output signals are attributable to respective beam paths traversed by the radiation through the body.
In recent years it has been proposed to apply computed tomography apparatus to examination of organs of a body in a relatively stationary condition. Such a method and system are described in U.S. Pat. No. 4,182,311 issued to Edward J. Seppi et al.
Raw projection data is collected during one or more continuous cycles of rotation while scanning, the acquired data is stored for use in the reconstruction process and is identified positively with portions of the organ cycle, and the desired cross-sectional image is reconstructed by correlating the stored data with the portion or phase of the cyclic movement of the body organ under examination.
The above apparatus has several disadvantages. In the conventional apparatus, only the projections are processed to reconstruct the image on the display device corresponding to a selected cardiac phase. However, unlike the present invention a series of reference electrocardiogram signals are not indicated on the same display device screen to show information correlated with the reconstructed image. Hence, it is impossible to simultaneously view the described cross-sectional image during the selected cardiac phase with the reference electrocardiogram information.
Furthermore there is no teaching nor suggestion of how the display device makes the information visible simultaneously on the same screen for convenient and comparative observation by an operator.